Doctor Blade Assembly

ABSTRACT

A doctor blade assembly for paper coaters and gravure rolls and other doctor blade applications includes a cantilever-support blade controlled by a tube-type actuator. The tube has a collapsible wall section adjacent the blade and a blade-engaging extension which bears against the blade between its supported and free end. In one embodiment, a transversely movable profile adjuster or series of profile adjusters are disclosed which selectively apply side forces to the wall section of the tube to permit corresponding selective pressure adjustments on the blade, for the purpose of reducing or eliminating localized coating nonuniformities. A novel blade retention assembly permits the clamping of blades of varying thicknesses and includes one or more transversely positioned magnets for temporarily retaining the blade on the support. An opposing clamp is formed with an elastomeric pad or expandable tube which engages the blade adjacent its inner edge and which forces or urges the blade downwardly against a machined seat to assure proper seating. In a further embodiment, a twin blade coater is disclosed in which the tips of the blades are independently rotatable about a common axis and which utilize a pair of the tube-type actuators connected to a common pressure source.

United States Patent [4 1 May 13, 1975 Zink [ 1 DOCTOR BLADE ASSEMBLY[75] Inventor: Stanley C. Zink, Fulton, NY.

[73] Assignee: The Black Clawson Company,

Middletown, Ohio [22] Filed: Jan. 11, 1974 [21] Appl. No.: 432,504

[52] US. Cl ..118/126; 118/122 [51] Int. Cl. B05c 11/04 [58] Field ofSearch 118/122, 123, 126, 413,

118/261; 117/102 L, 64 R, 64 C; 15/2566, 256.51

Primary Examiner--Morris Kaplan Attorney, Agent, or Firm-Biebel, French& Bugg [5 7] ABSTRACT A doctor blade assembly for paper coaters andgravure rolls and other doctor blade applications includes acantilever-support; blade contro1ledby a tube-type actuator. The tubehas aollapsible wall section adjacent the 'blade and a blade-engagingextension which [bears against'the blade between its supportedand free Anovel blade retention assembly permits the clamping of blades of varyingthicknesses and includes one or more transversely positioned magnets fortemporarily retaining the blade on the support. An opposing clamp isformed with an elastomeric pad or expandable tube which engages theblade adjacent its inner edge and which forces or urges the bladedownwardly against a machined seat to assure proper seating.

In a further embodiment, a twin blade coater is disclosed in which thetips of the blades are independently rotatable about a common axis andwhich utilize a pair of the tube-type actuators connected to a commonpressure source.

7 Claims, 10 Drawing Figures PATENIEU'MAY 31975 SHEET 18F 2 FIG-lgravure rolls, or the like. i g

In coating apparatus, it is important that the doctor blade be preciselypositioned and that the force applied to the blade be accuratelycontrollable in order to regulate the amount of material which isdoctored by the blade. Most commonly such blades are'used to control theweight of coating material which is applied to a moving web of paper.

In the past, it has been found advantageous to support a doctor blade atone end and to apply a controlled force between its supported end andits free end by the direct application thereto of one wall of an elastictube, to which a fluid pressure is applied. A successful embodiment isshown in the U.S. patent of Coghill U.S. Pat. No. 3,131,092 of 1964,assigned to the same assignee as this invention.

Among the references which were cited by the Examiner, during theprosecution of Coghill, the French Pat. No. 1,202,424 of 1959 (and itscorresponding British Pat. No. 863,426 may be cited out as showing atypical example of apparatus for applying a bladecoritrolling force bymeans of the direct contact of one wall of a flexible elastomeric tubeagainst the back side of the blade between its fixed support and itsfree end. Somewhat similar arrangements are shown in the U.S. patent ofFaber, U.S. Pat. No. 3,026,824 and Krautzberger U.S. Pat. No. 3,722,465of 1973. The latter additionally employs a thin leaf spring between thetube and the blade to compensate for a stated lack of uniformity offorce by reason of irregularities or lack of uniformity in the wallthickness of the force-applying tube.

The above described arrangements, and other like them, in which a tubeeffectively rests against the back surface of a blade, while generallysuccessful, suffer from the fact that the weight of coating which isapplied is often a non-linear function of the air pressure within thetube. One reason for this is that the tube may be operated in an elasticmode rather than in a partially collapsed mode, and therefore themodules of the tube must be considered. Another factor is thatinherently the contact region between the tube and the blade changes inlocation and in area during different operating conditions. For example,once the blade is in contact with the roller or the web, increasing thepressure will necessarily cause the adjacent wall of the tube toflatten, andat the same time, will cause the doctor blade to bendsomewhat. Thus, even though the movement of the tube wall may beconsidered as being a function of air pressure (which it usually is not)the changes in relative contact area and position necessarily result ina non-linear relationship.

One of the Coghillreferences, namely the U.S. patent of Fuchs U.S. Pat.No. 2,920,557 of 1960, shows an arrangement for doctoring a gravureroller which is intended to provide a more linearrelationship betweenair pressure and blade doctoringeffort, and includes, in

one embodiment,.a tube acting upon a transverse series of individualplungers, the remote ends thereof making the contact with the blade. Inanother embodiment, the plungers themselves are operated from individualfolding cylindrical diaphragms, and in either case the effort was toprovide a uniform relation. While this arrangement is theoreticallypossible, it suffers adversely in the complexity of the parts, requiringthe individual plungers. It also suffers from the fact of inherentnonuniformity in the transverse direction due again to the large numberof individual plungers positioned in sideby-side relation, and whichlack the continuous contact afforded by the direct contacting flexibletube.

. Flexible tubes have also been used in blade clamps and have been usedin pivot-supported blades as shown in the U.S. patents of Curtis U.S.Pat. No. 2,445,135 of 1948, Allison U.S. Pat. No. 3,085,275 of 1963 andWinterburn U.S. Pat. No. 3,748,686 of 1973.

SUMMARY OF THE INVENTION In one aspect of this invention, many ofthedifficulties and deficiencies of the prior cantilever-supported andtube-actuated blades are overcome by the provision of an elongatedflexible tube member which is formed with a flexible, collapsible wallsection positioned adjacent the blade and which is integrally formedwith a blade-engaging extension which engages the blade at a definedlocation or'region. The flexible wall section acts similarly to arolling diaphragm actuator except that it is transversely uniformthroughout the length of the tube and thus presents, in the manner of adiaphragm actuator, a relatively constant area to the application offluid pressure. Thus, the force exerted by the flexible wall sectionvaries uniformly with air pressure applied to the tube. It is alwaysoperated in a partially collapsed state; that is it is never operated tothe point where the tube itself becomes elastically expanded.

The integral extension which is formed on'the flexible wall thus definesand predetermines the contact region on the blade. Since this remainsconstant, a fluid pressure operated doctor arrangement is provided inwhich the weight of coating or the amount of ink doctored on an etchedroller, is a direct function of air pressure applied to the tube.

Accordingly this invention lends itself to automatic control, in effect,closing the loop of a control system, by applying pressure from acontrollable regulated source of fluid pressure. In addition, a furtheradvantage resides in the fact that an increased extent of overall blademovement is provided over that of the prior flexible tube arrangements.

One of the importantadvantages of the present invention is that theelastomeric linear actuator which is used provides for a relatively longstroke and accordingly provides for an increased wear compensation ascompared to the coaters in which one wall of the tube itself is used forblade pressure control. Additionally, the arrangement provides improvedsensitivity of blade control at lower air pressures.

A further" feature of the invention includes an improved arrangement formaking profile adjustments at transverse locations on the machine. Aspecial profile adjuster is disclosed which applies localized sideforces to one or both walls of the tube-type adjusters, to cause thematerial on the adjusters to bear with greater force against the blade,for the purpose of making localized adjustments in the'weight' ofcoating, such as for removarrangement may be the same as that which hasbeen disclosed for rotating an air knife about the region of impingementin the U.S. patent of Phelps, U.S. Pat. No. 2,981,224 of 1969 assignedto the same assignee as this invention.

A further aspect of the invention provides a twinblade coater in which apair of blades are positioned at opposite sides of a web with the tipsthereof forming a common apex. The tube-type actuators are employed foreach blade connected to a common source of air pressure. Additionally,mounting means are provided by which the blades are each adjustablethrough an axis in common with the apex.

In another aspect of the invention, an improved blade seating andholding arrangement is provided by means of which the doctor blade istemporarily supported in the holder and then is clamped into apredetermined seated relation on a machined surface. The temporaryholding means comprises one or more transversely arranged magnets whichclamp the metal blade and retain it in approximate position. When arelatively movable holding clamp comes in, a transverse elastomeric pador tube engages the blade just above the machined ledge and whenclamping pressure is applied, as by closing the clamp or inflating thetube a downward component of force is applied to assure that the bladefully seats against its mating surface.

It is accordingly an important object of this invention to provide anapparatus which uniformly controls the force of a doctor blade.

Another important object is the provision of a doctor blade actuator, asoutlined above.

A still further object is the provision of a tubeactuator provided witha flexible wall and an extension so that the region of force applicationto a cantileversupported blade does not change and so that the appliedforce is a substantially uniform function of applied fluid pressure.

Another object of the invention is the provision of an improvedarrangement for retaining and holding a doctor blade, in which a bladeseating force is applied to the blade by the blade clamp and in whichblades of differing thicknesses may be accommodated.

A further object is the provision of a twin-blade coater in which eachblade is acted upon by a tube-type actuator, as defined above. Inaddition, the blades are mounted for adjusting angular movement about anaxis which includes the apex formed by the blades.

Another object of the invention is the provision of an improved profileadjuster which is movable transversely of the width of the machine andwhich provides for varying the force of the blade at localized regionsby applying pressure to the flexible wall of the tube actuator.

These and other objects and advantages of the invention will be apparentfrom the following description, the accompanying drawings, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an end elevation, partiallyin section, of a blade coater constructed according to this invention;

FIG. 2 is a transverse fragmentary section of a portion of the coater ofFIG. 1 showing the actuator in the fully retracted position;

FIG. 3 is an enlarged fragmentary cross section showing the actuator inengagement with the doctor blade in an intermediate position;

FIG. 4 is a view similar to FIG. 3 but showing the actuator in its fullyextended position;

FIG. 5 is a fragmentary isometric view of the actuator showing theconnection to the regulated air pressure;

FIG. 6 is an enlarged fragmentary section showing a modified bladeclamping arrangement;

FIG. 7 is a broken away front elevation of a modification of the coater,providing for profile adjustments;

FIG. 8 is an enlarged side view of one-of the profilers;

FIG. 9 is the diagram of the invention as applied to a twin bladecoater; and

FIG. 10 is a fragmentary detail of the pivotal structure for supportingthe blades of the embodiment of FIG. 9.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIG. 1, a bladetype coater is shown in which a doctor blade 10 is cantilever-supportedand is urged against the exposed surface of a moving web 12, supportedon a backing roll 13. The arrangement shown in this embodiment is thusessentially the general type of coater as described in the Coghillpatent above. The coating material may thus be supplied from anysuitable downstream chamber or roll applicator. Also, a fountainapplicator may be employed as described in the U.S. patents of Coghill,U.S. Pat. Nos. 3,418,970 and 3,521,602. Additionally, the blade 10 maybe employed to doctor ink off of an etched gravure roller or may consistof a roll cleaning doctor.

Blade supporting means includes a relatively fixedtransversely-elongated blade support member 15. A movable clamp member16 is adjustable mounted on pivotally mounted arms 18. The arms 18 turnabout pivots 20 as shown in FIG. 1. A fixed support provides support forboth the fixed blade support member 15 and the arms 18, and alsosupports a diaphragm type motor 26. The rod end 27 on the motor isconnected to apply a closing force to the clamp member 16. It isunderstood that two or more fixed supports 25 and motors 26 arepositioned transversely on the coater with associated arms 18 to provideopening and closing movements to the clamp member 16.

One of the aspects of the present invention relates to means by whichthe blade 10 is fixed in predetermined alignment. The clamp member 16and the fixed blade support 15 together comprise one embodiment of animproved blade holder assembly for a flexible coater blade. The supportmember 15 is formed with a bladereceiving wall 30 for supporting onesurface of the metallic blade 10. The wall 30 is terminated in amachined ledge 32, as shown in FIG. 2, for receiving the bottom edge ofthe blade 10.

Means for temporarily supporting the blade 10 against the wall 30 priorto the closing of the clamp includes a transverse series of individualmagnets 35. The magents may be ringshaped and received in recessesformed in the member 15 and retained by retainer screws 36.

In the embodiment of FIG. 2 the movable clamp member 16 is provided witha transversely extending elastomeric blade engaging pad 40. The padextends continuously the width of the member 16 and is positioned toengage the opposite surface of the blade 10 adjacent the ledge 32 uponclosing movement of the clamp 16 as caused by the diaphragm motors 26.The pivot point 20 of the arms 18 is shown as being transversely offsetwith respect to the plane of the wall 30 so that when the pad 40 comesinto engagement with the blade 10, the closing force is accompanied by adownward component of force which tends to urge the blade firmly againstthe seat or ledge 32. In this manner, the blade 10 is held bycompressive force on the pad 40 against the wall 30 and in engagementwith the ledge 32. The compressive force is uniform through out thewidth of the coater and therefore any tendency for warpage of the blade10 is eliminated.

It is understood that either member or 16 may be the moving or clampingmember. Also, the arrangement automatically accommodates blades ofdiffering thicknesses, such as .010 .020, or .030 inch thicknesses, forexample.

In changing or inserting a blade, the member 16 is retracted on the arms18 and the blade is inserted against the wall 30 and on the ledge 32. Itis retained by the magnets 35. The clamp member 16 is then brought intothe closed position shown in FIG. 2 and a clamping or closing force isapplied by the motors 26. Since the pivot point on the arms 18 is offsetwith respect to the plane of the wall 30, a downward component of forceis applied to the blade 10 by the pad 40 causing the blade to be firmlyset on the ledge 32 and thus pre cisely located.

In FIG. 6 there is illustrated a somewhat modified arrangement forclamping and supporting the blade 10. Instead of the pad 40, a modifiedtube support or clamp member 15 is provided with a semi-cylindricalrecess to receive a conventional clamping tube 42. The tube 42 may be ofthe general type shown in the Coghill patent and identified therein byreference number 27. However, the tube support 15' is relieved asindicated at 43 adjacent the lower edge of the tube so that the forceexerted by the tube is both outward and somewhat downward in relation tothe plane of the blade 10, thus causing the blade to be firmly urgedagainst the seat 32 as in the embodiment of FIGS. 1 and 2.

As previously mentioned, the clamping arrangement of this inventionprovides a cantilever-supported blade which, in the embodiment of FIG.1, is urged against the web 12 to control the weight of the coatingapplied thereto. Thus, certain considerations become important. First,it is desirable that the blade 10 be controlled with precision and it isfurther desirable that the position of the blade be controlled to makeup and compensate for blade wear. Since coatings are inherentlyabrasive, the blade 10 will wear and thus it is important that wearcompensation be provided without substantially changing thecharacteristics of the coater. In this connection, it is preferred thatthe blade support assembly, including the parts 25, 15, and 16, bemounted on cross-machine supports which permit the blade 10 to bechanged in angular relation to the web 12. The mounting preferred isthat shown in the aboveidentified Phelps patent for an air doctor, whichpermits the blade to be pivoted about an axis coinciding with its freeor web-engaging edge.

The doctor blade of this invention includes a transversely-elongatedflexible tube-type actuator indicated generally at 50. The actuator ismounted on the clamp member 16 by a transverse support 52, the positionof which is adjustable by a series of individual micrometer adjusters55.

The support 52 is provided with a forwardly-opening,transversely-elongated support channel 58 which receives and supports atthe actuator 50. It is understood that the actuator tube is hollow andis adapted to receive fluid pressure therein. It is formed with arelatively thick and semi-rigid back 60 which is received within thechannel 58. The actuator 50 is further pro vided with a collapsiblefront wall section 62 which is positioned adjacent the front surface ofthe blade 10. The wall section 62 is movable between a retracted,partially-folded condition as shown in FIG. 2 in which it lies in closeproximity to the back 60, to an extended and substantially roundedcondition as shown in FIG. 4 when fluid pressure is applied thereto. Theactuator 50, in effect, forms a transversely-elongated bellows typelinear actuator, and it is operated with the wall section 62 always in astate of flexure, and not in a stretched state.

The wall section 62 is formed with a blade-engaging extension 65 formedintegrally therewith and terminated in transverse serations 66. Theextension 65 is formed substantially centrally on the wall section andis thus movable with the wall section 62. Only the extension 65 engagesthe blade 10, and as shown, it engages the blade between its supportedand free ends to apply a doctoring force thereto. A suitable source forthe actuator tube material consists of pressure seal PRS-581 of PresrayCorporation, 159 Maple Blvd., Pawling, New York 12564.

Since the actuator 50 is always operated in a flexed condition, theeffective area of the wall section 62 which is subject to pressure withthe tube reamins substantially constant with the movement of the wallseeiton. Additionally, the location of engagement of the extension 65 onthe blade 10 remains substantially constant. In this manner, thedoctoring effort of the blade 10 varies approximately as a directfunction of fluid pressure, and the weight of coating variesapproximately as an inverse function of pressure.

As shown in FIG. 5, the ends of the acuator 50 are closed and aregulated source of fluid pressure through a pressure regulator isapplied substantially at the center of the actuator through an inletfitting 72. Preferably, air is used although other sources of fluidpressure, even a liquid with an accumulator, could be used.

The actuator arrangement of the present invention provides for precisecontrol. For example, 2 PSI. of pressure may be used to bring theextension 65 into contact with the blade 10. Another 2 to 3 pounds ofpressure may be employed to extend the actuator to its full stroke asshown in FIG. 4. The use of an actuator having a folded or folding wallpermits up to a threequarter inch stroke, which is substantially morethan can be achieved by using the wall of a rounded tube as an actuator.In addition, the location of engagement of the actuator with respect tothe blade remains constant for any engagement condition. Thus, thedoctoring force may be increased or decreased without any change incontact position or area, providing for precise control. If desired, theregulator 70 may be automatically controlled by downstream sensors toregulate the weight of coating.

In some instances it may be desirable to apply a localized correctingpressure to the doctor blade 10 in order to eliminate a wet area orstreaking or other crossmachine coating irregularities. For thispurpose, there is shown in FIGS. 7 and 8 a profile arrangement by meansof which localized pressure may be applied to the blade at selectedtransverse locations to cause the blade to engage the web with a forcewhich somewhat exceeds that effected by the fluid pressure alone. Forthis purpose, a modified Combined clamp and tube support 80 may be usedwhich serves both as the blade clamping member as identified above andas the support and backing member for the tube 50. The support 80 isshown as having a wall support section 82 which in partial engagementwith one of the side walls 62 of the tube but which permits the Walls toflex outwardly freely to bring the extension into engagement with theblade.

A transversely movable profile assembly 85 is mounted on the member andis adjustably supported thereon by a clamp portion 86 engaging anL-shaped support 87. The profile assembly includes an adjustablepivotally mounted finger 90 which has an extended end 92 which engagesthe opposite flexible wall of the tube 50. The force by which the end 92engages the tube may be regulated by a thumb screw 95. When it isdesirable to apply a corrective or profile force, one or more of theassemblies 85 may be attached to the support 80 and the finger 90brought into position. The force exerted by the finger 90 against thecombined wall sections of the tube 50 causes the tube in the localizedtransverse region to be urged outwardly against the blade with a forcewhich is greater than that which would be effected by the fluid pressurealone. The profile assembly 85 may have any convenient width, such as,for example, 4 inches, and several may be used at one time, if required.

The precise control which is afforded by the present inventionparticularly adapts the same to a twin blade coater, as diagrameticallyillustrated as FIGS. 9 and 10. A pair of identical,diagrametically-opposite flexible blades and 102 are supported onidentical holder assemblies 105, which may be as described above inconnection with FIGS. 1 and 2 or FIGS. 7 and 8. Each of the blades 100and 102 is operated by a separate pressure actuator 50 constructed aspreviously described. The actuators 50 are connected to a common sourceof fluid pressure as diagrametically illustrated by the lines 110. Theblades 100 and 102 form a common apex and thus simultaneously engage theopposite surfaces of the'moving web which has been run through a coatingbath 118. It is critically important that the position of the blades 100and 102 be maintained so that the forces across the blades are balancedand so that the tips of the blades form a true apex with respect to theweb 115. The employment of the sensitive actuator as described and theuse of a common source of air pressure assures that each blade 100 and102 will be acted upon with the same force.

It is also important that the blades 100 and 102 be mounted so that theycan be pivoted about a common axis which includes the apex or tips ofthe blade, independently of each other, such as through a 15 angle forexample. One suitable arrangement for this is to provide blade supportarms and 121, at the extreme sides of the machine, with a common pivot124. The pivot axis defined by the pivot 124 is substantially coincidentwith the apex 125 formed by the blades. In this manner, propercoincidence of the blades is assured throughout adjustments inangularity with respect to the web 115.

While the forms of apparatus herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention.

What is claimed is:

1. In a blade type coater in which a cantileversupported blade is urgedagainst a moving web to control the weight of the coating appliedthereto, the improvement comprising a transversely elongated flexibletube, means supporting said tube adjacent said blade between thesupported end and the free end thereof, said tube being formed with acollapsible wall section adjacent said blade and a blade-engagingextension which is formed with an integral part of said wall section,said extension being movable by said wall section transversely of saidtube upon the application of fluid pressure thereto and engageable withsaid blade at a relatively fixed location on said blade, the effectivearea' of said wall section subject to pressure remaining substantiallyconstant with movement of said wall section, and the location on saidblade upon the application of force by said extension remainingsubstantially constant so that the weight of coating applied variesapproximately as an inverse function of fluid pressure applied to saidtube, and pressure regulating means for applying a regulated fluidpressure source to the interior of said tube.

2. The coater of claim 1 further comprising a second saidcantilever-supported blade positioned to engage said Web at the oppositesurface thereof and at a diametrically opposed position relative to thefirst blade, and a second said flexible tube having its extensionpositioned to engage said second blade in the same manner as defined inclaim 1, each of said tubes being connected to said pressure source sothat each of said blades are thereby affected uniformly and urged withequal force against said web.

3. In a blade type coater, a transversely elongated cantilever-supportedblade, a transversely elongated tube, means supporting said tubeadjacent said blade between the supported end and the free end thereof,said tube having a flexible, collapsible wall section adjacent saidblade, a transversely extending bladeengaging extension formedsubstantially centrally of said wall section and movable by said wallsection upon the application of fluid pressure thereto and engageablewith said blade at a relatively fixed location on said blade, theeffective area of said wall section subject to pressure remainingsubstantially constant with movement of said wall section, and theposition of said extension on said blade upon the application ofpressure to said tube remaining substantially constant so that theweight of coating applied varies approximately as an inverse function offluid pressure applied to said tube, and pressure regulating means forapplying a regulated fluid pressure source to the interior of said tube.

4. In a blade doctor assembly, a blade, means supporting said blade atone end, a flexible tube, means supporting said tube extending adjacentsaid blade between the supported end and the free end thereof, said tubebeing formed with a collapsible wall section adjacent said blade and ablade-engaging extension which is formed as an integral part of saidwall section, said extension being positioned centrally of said wallsection andmovable by said wall section upon the application of fluidpressure to said tube and engageable with said blade at a relativelyfixed location on said blade, the effective area of said wall sectionsubject to pressure remaining substantially constant with movement ofsaid wall section, and the location on said blade upon the applicationof force by said extension remaining substantially constant so that thedoctoring effort of said blade is a direct function of air pressureapplied to said tube, and air pressure regulating means for applying aregulated air pressure source to the interior of said tube.

5. The assembly of claim 4 further including means for making profilecorrections in blade doctoring forces, comprising at least oneadjustable means engageable with said wall section at opposite sides ofsaid extension for confining said wall section at a selectabletransverse location to urge said extension against said blade with aforce which exceeds that applied by the fluid pressure alone.

6. A blade type coater having improved sensitivity and blade wearcompensation, comprising a doctor blade, means supporting said bladealong one transverse edge thereof, said blade having a free doctoringedge, a transversely elongated tube-type fluid pressure actuator, saidactuator having a relatively rigid back and having a front wall sectionwhich is movable from a retracted, partially-folded condition in which aportion thereof lies in close proximity to said back and an extended,substantially rounded condition with the application of fluid pressurethereto, a transversely elongated blade-engaging extension formed as anintegral. part of said wall section and movable therewith, meanssupporting said actuator with said extension in engagement with saidblade between its supported edge and free edge to urge said blade withincreasing doctoring effort with extending movement of said'wallsection, the region of engagement of said extension on said bladeremaining relatively fixed with changes in fluid pressure in saidactuator, and means for applying fluid under regulated pressure to saidactuator to control the weight of coating and to compensate for wear ofsaid blade.

7. The coater of claim 6 further comprising an adjuster for effectingprofile corrections, means mounting said adjuster on said blade supportmeans, said adjuster having a movable portion engageable with saidactuator at said wall section to apply a force thereto at a localizedregion thereof in g a direction normal to the transversely-elongateddirection of said actuator, said adjuster being effective to cause saidextension to be urged with somewhat increased force at said localizedregion against said blade.

1. In a blade type coater in which a cantilever-supported blade is urgedagainst a moving web to control the weight of the coating appliedthereto, the improvement comprising a transversely elongated flexibletube, means supporting said tube adjacent said blade between thesupported end and the free end thereof, said tube being formed with acollapsible wall section adjacent said blade and a blade-engagingextension which is formed with an integral part of said wall section,said extension being movable by said wall section transversely of saidtube upon the application of fluid pressure thereto and engageable withsaid blade at a relatively fixed location on said blade, the effectivearea of said wall section subject to pressure remaining substantiallyconstant with movement of said wall section, and the location on saidblade upon the application of force by said extension remainingsubstantially constant so that the weight of coating applied variesapproximately as an inverse function of fluid pressure applied to saidtube, and pressure regulating means for applying a regulated fluidpressure source to the interior of said tube.
 2. The coater of claim 1further comprising a second said cantilever-supported blade positionedto engage said web at the opposite surface thereof and at adiametrically opposed position relative to the first blade, and a secondsaid flexible tube having its extension positioned to engage said secondblade in the same manner as defined in claim 1, each of said tubes beingconnected to said pressure source so that each of said blades arethereby affected uniformly and urged with equal force against said web.3. In a blade type coater, a transversely elongated cantilever-supportedblade, a transversely elongated tube, means supporting said tubeadjacent said blade between the supported end and the free end thEreof,said tube having a flexible, collapsible wall section adjacent saidblade, a transversely extending blade-engaging extension formedsubstantially centrally of said wall section and movable by said wallsection upon the application of fluid pressure thereto and engageablewith said blade at a relatively fixed location on said blade, theeffective area of said wall section subject to pressure remainingsubstantially constant with movement of said wall section, and theposition of said extension on said blade upon the application ofpressure to said tube remaining substantially constant so that theweight of coating applied varies approximately as an inverse function offluid pressure applied to said tube, and pressure regulating means forapplying a regulated fluid pressure source to the interior of said tube.4. In a blade doctor assembly, a blade, means supporting said blade atone end, a flexible tube, means supporting said tube extending adjacentsaid blade between the supported end and the free end thereof, said tubebeing formed with a collapsible wall section adjacent said blade and ablade-engaging extension which is formed as an integral part of saidwall section, said extension being positioned centrally of said wallsection and movable by said wall section upon the application of fluidpressure to said tube and engageable with said blade at a relativelyfixed location on said blade, the effective area of said wall sectionsubject to pressure remaining substantially constant with movement ofsaid wall section, and the location on said blade upon the applicationof force by said extension remaining substantially constant so that thedoctoring effort of said blade is a direct function of air pressureapplied to said tube, and air pressure regulating means for applying aregulated air pressure source to the interior of said tube.
 5. Theassembly of claim 4 further including means for making profilecorrections in blade doctoring forces, comprising at least oneadjustable means engageable with said wall section at opposite sides ofsaid extension for confining said wall section at a selectabletransverse location to urge said extension against said blade with aforce which exceeds that applied by the fluid pressure alone.
 6. A bladetype coater having improved sensitivity and blade wear compensation,comprising a doctor blade, means supporting said blade along onetransverse edge thereof, said blade having a free doctoring edge, atransversely elongated tube-type fluid pressure actuator, said actuatorhaving a relatively rigid back and having a front wall section which ismovable from a retracted, partially-folded condition in which a portionthereof lies in close proximity to said back and an extended,substantially rounded condition with the application of fluid pressurethereto, a transversely elongated blade-engaging extension formed as anintegral part of said wall section and movable therewith, meanssupporting said actuator with said extension in engagement with saidblade between its supported edge and free edge to urge said blade withincreasing doctoring effort with extending movement of said wallsection, the region of engagement of said extension on said bladeremaining relatively fixed with changes in fluid pressure in saidactuator, and means for applying fluid under regulated pressure to saidactuator to control the weight of coating and to compensate for wear ofsaid blade.
 7. The coater of claim 6 further comprising an adjuster foreffecting profile corrections, means mounting said adjuster on saidblade support means, said adjuster having a movable portion engageablewith said actuator at said wall section to apply a force thereto at alocalized region thereof in a direction normal to thetransversely-elongated direction of said actuator, said adjuster beingeffective to cause said extension to be urged with somewhat increasedforce at said localized region against said blade.